Steam generator



March 21, 1961 Heat 5 o urea H. O. MONSON STEAM GENERATOR Filed Jan. 19,

Reservoir INVENTOR. f/affj/ 0 M01250 United States Patent STEAM GENERATOR Harry 0. Monson, Elmhurst, 111., assignor to the United States of America as represented by the United States Atomic Energy Commission Filed Jan. 19, 1959, Ser. No. 787,784

'3 Claims. (Cl. 122-33) This invention relates in general to steam generating apparatus and in particular to a method and apparatus for transferring indirectly heat from one liquid medium to another liquid medium.

. The method and apparatus to be described herein is particularly directed to power-plant equipment utilizing an alkali metal-coo1ed neutronic reactor as a heat-producing source. A reactor of this type utilizes an arrangement of different materials including fissionable material to obtain a self-sustaining chain reaction to produce useful heat from the fission process whereby the heat is removed by a molten alkali metal coolant, such as sodium or potassium, and transferred therefrom to another medium such as water, to produce steam useful in production of power. As is Well known, the reaction of the alkali metals with water is energetic and explosively rapid when the contact interfaces are large. As a result, the heat-exchange equipment has to be very carefully constructed and tested to eliminate all possibilities of leaks. But even then, there exists the probability that at some time a rupture may occur in the heat exchange equipment and allow the alkali metal to react violently with the Water with consequent destruction of the equipment and exposure of operating personnel to danger.

It is the object of this invention to provide a method for safely transferring heat from an alkali metal medium to a water medium.

It is another object of the invention to provide means in heat exchange relationship with an alkali metal and water, to transfer heat between said fluids without danger resulting from possible contact resulting between them.

A further object of the invention is to transfer heat from alkali metal to water by indirect means so that liquid water and sodium are never found in the same vessel.

Another object of the invention is to provide means for safely transferring heat from alkali metal medium to water by indirect means so that the alkali metal medium and the water are not in a heat exchange relationship.

A further object of the invention is to provide a method for safely transferring heat from an alkali metal to water through a steam phase.

Another object of the invention is to provide means for transferring heat from an alkali metal to Water without any attendant danger due to accidental direct contact between them.

Other objects of the present invention will be apparent from the description which follows:

In accordance with the teaching of this invention, there is provided a method for indirectly transferring heat from a molten alkali metal, such as sodium, potassium or sodium-potassium alloys, to Water, comprising the steps of heating the water to generate steam, transferring heat from the alkali metal to the steam to superheat it, and transferring heat from some of the superheated steam to the Water to generate additional steam while using the rest of the superheated steam for some purpose such as Patented Mar. 21, 19 61 the production of power. The aforesaid method is carried out by a boiler, a superheater in which molten alkali metal superheats steam from the boiler, and piping carrying superheated steam back and forth repeatedly between the superheater and the boiler to generate additional steam and to reheat the superheated steam.

The advantages of the apparatus and method of the present invention will be fully understood from the following description and single figure of drawing schematically illustrating the apparatus of the present invention.

A heat source 26, such as a nuclear reactor, is connected to a superheater 28 by pipes 30 and 32 conducting a molten alkali metal between the heat source and the superheater. A water boiler 34 is connected through a pipe 36 and a valve 38 to a reservoir 40 which is supplied with water by a pump 42 connected through a pipe 44 to a condenser 46 which is connected to a turbine 48. The reservoir 40 is also fed by a pump 50 connected to a condenser 52 which receives spent steam through a pipe 54 and a valve 56, leaving the boiler 34. The boiler 34 supplies steam to the superheater 28 through a pipe 58 and a valve 60. A pipe 61, which has a valve 62, leads from the superheater 28 to the turbine 48. The turbine 48 is supplied with most of the steam emerging out of the superheater 28. To the pipe 61 is connected a means 64 for piping a portion of the superheated steam issuing from the superheater 28 back and forth in repeated passes alternately through the boiler 34 and the superheater 28, and the last pass through the boiler 34 is connected with the pipe 54. Because of the rather unusual structure of superheater 28 with flowing molten alkali metal on its shell-side which transmits heat to the steam in pipe 58 which is one tube-side, and also to the steam in the bank of tubes of the pipe convolutions between it and the water boiler, which constitutes a second tube-side, it may be referred to as a double tube-sided heat exchanger, in distinction to conventional single tubesided heat exchangers which exchange heat between only two bodies of fluids from the shell-side to a single tubeside. There is a valve 66 in the portion of the piping means 64 between the pipe 61 and the first pass through the boiler 34. The valve 62 is used to control the amount of superheated steam passing into the turbine 48, and the valve 66 is used to control the amount of superheated steam by-passed for steam generating purposes in the water boiler 34. A heater element 76, disposed in the water boiler 34, is used to initiate steam during start-up. The heater element may be connected to any convenient source of heat.

The steam producing equipment described hereinbefore, may be put into operation in the following way, The water contained in the water boiler 34 may be heated by the heater element 76 to produce steam which is subsequently withdrawn through the pipe 58 and valve 60 into the superheater boiler 28. Assuming that the system has been brought to the stage of producing steam under controlled rate in the Water boiler 34, the steam is passed through the pipe 58 and the valve 60 into the superheater 28, wherein said steam becomes superheated by absorbing additional heat from the molten alkali metal circulated in the superheater 28. Most of the superheated steam passes out of the superheater 28 and is used by the turbine 48 to produce power. The portion of the superheated steam flowing through the piping means 64'gives up heat to the water in the boiler 34 in each pass therethrough and regains heat from the molten alkali metal in the superheater 28 in each pass therethrough. The flow rate of the steam through the piping means 64 is controlled so that the steam loses only a limited amount of heat in each pass in the boiler 34 and thus condenses little if at all before returning to the superheater 28 for reheating. After the final pass in the v 3 piping means 64 through the boiler 34, the steam passes out of the boiler through the pipe 54 and the valve 66 into the condenser 52, where it is condensed and. then pumped by the'pump' 50 intothe reservoir 40. The spent steam from the turbine 48 is condensed in .the condenser 46, and then the condensate is moved by the pump'42 into the reservoir'40. The drawing appearsto show the piping mean'sr64as having three passes through the boiler 34 and two passes through the superheater 28, but the apparatus of the present invention will not function with less. than four. passes of the'piping means 64 through the boiler 34'if, for example, superheated steam is delivered to the turbine 48 at 1250 lbs. gage'and 850 F. and the feedwater is supplied to the boiler 34 at 500 lbs. gage and 480 F. Under these conditions about 90% of thesuperheated steam leaving the superheater 28 through thepipe- 61 will have to go to the boiler 34 through the piping means 64 and only will go to the turbine 48. It ismost desirable that the greater portion of the superheated steam in the pipe 61 go to the turbine 48, and this requires that the passes of the piping means 64 through the boiler 34 be increased. Forty passes through the boiler will give very good results. Theoretically, an infinite number of passes through the boiler gives the best results, for increasing the number of passes decreases the heat abstraction per pass through the boiler and thus the tendency to condense. As a practical matter, triction losses that reduce the pressure in the pipe 54 below a feasible level limit the number of passes through the boiler, because reducing the friction lossper pass increases the diameter of the passes, with the result that there is a large number of passes all with a large diameter and the boiler 34 is too large.

The advantage in the apparatus of the present invention is that heat is transferred directly from molten alkali metal to steam, rather than to water, and so any leaks will result in the mixing of alkali metal and steam, which is relatively safe, rather than in the mixing of alkali metal and water, which is potentially dangerous. Yet, with this arrangement the alkali metal is still used to convert water to steam.

, The invention is to limit the invention only the scope of the appended claims.

What is claimed is:

1. Apparatus for transferring heat from a molten alkali metal to water in order to produce superheated steam, comprising a reservoir for water in the liquid state, a connection. between the reservoir and a water boiler, a water boiler having a shell and within the shell a start-up heater and a sufliciently plurality of closed parallel conduit convolutions to carry steam to convert aormvo to vapor, by heat diffusion, the water within the shell and exterior to the start-up heater and the conduit convolutions, a connection between the shell of the boiler and through the shell of a heat exchanger, a double tubesided heat exchanger having a shell and within the shell flowing molten alkali metal, a first tube-side joined to the connection from the shell of the boiler of sufiicient 1 length to permit heat from the alkali metal to convert the vapor from the boiler to superheated steam, and a second tube-side consisting of a plurality of" closed parallel conduit convolutions equalg in number to the plurality of conduit convolutions within the boiler, the two pluralities being joined by a like plurality of connections in series as to form a continuous conduit running alternately through the boiler and the heat exchanger, an outlet for the first tube-side leading through the shell of the heat exchanger to a pipe junction, a pipe junction having a first branchv and a second branch, said first branch making exterior delivery or'rhesu erheated steam' produced by the apparatus, means for returning the condensate of said superheated steam to the reservoir, said second branch having a valve for controlling the respective amounts of steam passing through the two branches, said-secondbr'anch leading to said continuous conduit running alternately through the boiler and the heat exchanger through said pluralities of conduit convolutions, whereby heat isabsorbed from the steam by the liquid water in the boiler and replaced by heat absorbed by the steam fromthe molten alkali metal in the heat exchanger, means for leading steam from the last of the series of conduit convolutions to a condenser, a condenser, and means'for' leading the condensate produced by the condenser into the reservoir.

2. The apparatus of claim 1 where the number of conduit convolutions through the boiler and through the superheater is forty.

3. The apparatus of claim 1 where a steam turbine, a condenser and a pumping means. are intermediate the exit of the first branch of the conduit junction and the reservoir, and a second pump is intermediate the condenser in the second branch and the reservoir.

References Cited in the file of this patent UNITED STATES PATENTS 1,944,059 Baumann Jan. 16, 1934 2,291,195 Stieger July 28, 1942 2,878,644 Fenn Mar. 24, 1959 2,893,701 Bell July 28, 1959 FOREIGN PATENTS 1,168,927 France Sept, 8, 1958 

